Electrostatic reproduction involves an electrostatically-formed latent image on a photoconductive member, or photoreceptor. The latent image is developed by bringing charged developer materials into contact with the photoconductive member. The developer materials can include two-component developer materials including carrier particles and charged toner particles for such as “hybrid scavengeless development” having an image-on-image development. The developer materials can also include single-component developer materials including only toner particles. The toner particles adhere directly to a donor roll by electrostatic charges from a magnet or developer roll and are transferred to the photoconductive member from a toner cloud generated in the gap between the photoreceptor and the donor roll during the development process. The latent image on the photoreceptor can further be transferred onto a printing substrate.
During the printing process, one challenge is how to reliably and efficiently move charged toner particles from one surface to another surface, e.g., from carrier beads to donors, from donors to photoreceptors, and/or from photoreceptors to papers, due to toner adhesion on surfaces. For example, distributions in toner adhesion properties and spatial variations in surface properties (e.g. filming on photoreceptor) of the adhered toner particles lead to image artifacts, which are difficult to compensate for. Conventional solutions for compensating for these image artifacts include a technique of image based controls. However, such technique mainly compensates for the artifacts of periodic banding. To compensate for other artifacts such as mottle and streaks, conventional solutions also include a mechanism of modifying the toner material state using maintenance procedures (e.g., toner purge), but at the expense of both productivity and run cost.
In addition, for today's non-contact development subsystems, the image fields are insufficient to detach toner particles from the donor roll and move them to the photoreceptor. For example, conventional donor rolls use wire electrodes to generate toner clouds. Generally, AC biased wires have been used to provide electrostatic forces to release the toner particles from the donor roll. However, there are several problems with wires. First, toner particles tend to adhere to the wires after prolonged usage even with a non-stick coating on the wires. The adhered toner particles may cause image defects, such as streaks and low area coverage developability failures. Second, it is not easy to keep the wires clean once the wires are contaminated with toner components. The wires thus need frequent maintenance or replacement. Third, depending on the printing media and image, adhesion forces vary along the surface of the development and transfer subsystems Use of wires makes it difficult to extend the development for wide-area printing.
Thus, there is a need to overcome these and other problems of the prior art and to provide a roll member having image-wise addressability used as a replacement to wires to control toner quality and to provide a direct imaging system without using a photoreceptor.